The invention relates to forming, filling, and sealing plastic packaging.
In form, fill, and seal apparatus, a bottom web of plastic is advanced through a vacuum thermoformer (where the plastic web is formed to provide receptacles for receiving articles), a filling station (where articles are placed in the formed receptacles), a sealing station (where a top web made of plastic, paper, or other sheet material is placed over the filled receptacles and sealed to portions of the bottom web around the receptacles to provide covers), and a cutter (where the sealed top and bottom webs are cut at portions between receptacles into separate packages).
Normally the bottom web of plastic is driven through the thermoformer, filling station, and sealing station via continuous loop drive chains underneath the two side edges of the web. The top web is pulled by virtue of being sealed to the bottom web at the sealing station. The movement of the bottom and top webs typically is intermittent (often referred to as indexed), as the thermoform and fill operations are performed when the web is stationary. During each movement of the webs between the simultaneous form and fill operations at respective stations, both webs are of course accelerated and decelerated. The upper web passes from its supply roll around a weighted dancer, which assists in smoothing out stresses in the upper web. The dancer is lifted as the web is first drawn, and a brake mechanism prevents rotation of the supply roll except when the dancer has been raised to a particular position. Depending upon the tack between upper and lower webs at the seal and the amount of travel of each movement, the speed of the webs during indexing may have to be limited to avoid damage to the seal. E.g. weld seals are strong, are formed quickly, and can permit relatively fast pulling of the upper web. Seals for removable covers are weaker and may be destroyed if the lower web is moved too fast. Seals that take a long time to form and seals involving cover webs made of certain (e.g., fragile) materials may also be destroyed if they are moved too fast.